Commit 2800486e authored Sep 07, 2017 by Peter Zijlstra Committed by Ingo Molnar Sep 12, 2017

sched/fair: Avoid newidle balance for !active CPUs



On CPU hot unplug, when parking the last kthread we'll try and
schedule into idle to kill the CPU. This last schedule can (and does)
trigger newidle balance because at this point the sched domains are
still up because of commit:

  77d1dfda ("sched/topology, cpuset: Avoid spurious/wrong domain rebuilds")

Obviously pulling tasks to an already offline CPU is a bad idea, and
all balancing operations _should_ be subject to cpu_active_mask, make
it so.

Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Fixes: 77d1dfda ("sched/topology, cpuset: Avoid spurious/wrong domain rebuilds")
Link: http://lkml.kernel.org/r/20170907150613.994135806@infradead.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 46123355

kernel/sched/fair.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -8447,6 +8447,12 @@ static int idle_balance(struct rq this_rq, struct rq_flags rf)
		*/
		this_rq->idle_stamp = rq_clock(this_rq);

		/*
		* Do not pull tasks towards !active CPUs...
		*/
		if (!cpu_active(this_cpu))
		return 0;

		/*
		* This is OK, because current is on_cpu, which avoids it being picked
		* for load-balance and preemption/IRQs are still disabled avoiding

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